Staphylococcus aureus (S.aureus) is a formidable human pathogen responsible for severe infections in the hospitals and community. S. aureus produces a variety of virulence factors including a range of exotoxins with immune inhibitory, immunomodulatory, and cytotoxic activities. One of these toxins, the Panton Valentine Leukocidin (PVL), is a pore forming toxin associated with severe pneumonia cases of community acquired S. aureus infections. Current vaccine efforts targeting PVL are focused on single wild type subunits. However, this approach may pose serious safety concerns for human use. The overall goal of this research plan is to develop a recombinant, mutant (attenuated) and bivalent vaccine against PVL. The proposal is based on extensive structural analysis of the components of PVL and structure- based, rational design of potentially attenuated mutants. This Phase I SBIR is designed in two Specific Aims. In Aim 1 we will introduce point mutations into the genes encoding for the LukS and LukF subunits of PVL to abolish toxin oligomerization and the resulting pore formation, and characterize the integrity and activity of the mutant PVL subunits in vitro. The degree of attenuation of the vaccine candidates will be determined in vitro and in vivo. In Aim 2 we seek to further characterize and down-select mutant PVL subunits as vaccine candidate(s) based on efficacy studies using mouse challenge models of native PVL toxin and to perform preliminary evaluation in S. aureus infections in BALB/c mice using the MRSA clone USA300. The endpoint for the Phase I is the identification of one or two preclinical candidates. In Phase II of this SBIR we will complete the preclinical efficacy, formulation, and safety studies for the selected vaccine candidate(s). The ultimate goal is to develop a safe and effective PVL antigen that could be integrated into a multivalent S. aureus vaccine formulation that will include other toxins or cell- associated S. aureus antigens. PUBLIC HEALTH RELEVANCE: This proposal is aimed at development of a safe and effective vaccine for one the toxins produced by Staphylococcus aureus (SA), known as PVL. Antibiotic resistant SA infections have been on the rise in the past two decades both in the hospitals and in the community. There are currently no vaccine available against SA infections. PVL is known to play an important role in severe cases of pneumonia caused by community acquired MRSA. The vaccine produced under this program is expected to be a component of a multicomponent vaccine for prevention of SA infections.